We plan to do this feature. Currently, if you have an urgent business need for this feature, we can whitelist your non-default environment to allow gateway. You need to file a support ticket for this and we will evaluate carefully your request.

Same here, all of our flows and powerapps utilize gateway connections, making environments useless to us currently since we can't develop against these connections in any other environment except default. It would be great to be able to assign connections to an environment, or assign an entire gateway to an environment.

All of our apps are driven with on premise data from a SQL database. We would not be able to use diffrenet enviroments if we can't have access to the gateway in each environment for SQL dev connections, SQL test connections, etc.